move control of this variable to cam

[jedwards4b]

Description of changes

moves variable add_gusts from namelist_definition_drv.xml to namelist_definition_drv_flds.xml so that cam controls the settings.

Specific notes

Contributors other than yourself, if any:

CMEPS Issues Fixed (include github issue #):

Are changes expected to change answers? (specify if bfb, different at roundoff, more substantial)

Any User Interface Changes (namelist or namelist defaults changes)?

Testing performed

Please describe the tests along with the target model and machine(s) If possible, please also added hashes that were used in the testing